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Chapter 8 Environmental Aspects of Copper Production

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Chapter 8

Environmental Aspects ofCopper Production

CONTENTSPage

Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..................162Pollutants of Concern and Their Regulation . . . . . . . . . . . . . . . . ............162Smelter Pollution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163Costs and Benefits of Pollution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...168

Water Quality and Waste Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......170Pollutants of Concern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...............173Waste Management Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...174

BoxesBox Page8-A. Alternative Byproducts From the Control of Strong SO2 Emissions . ......1658-B. Collecting Converter Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........1688-C. The Resource Conservation and Recovery Act.... . ...................1738-D. Factors Affecting the Potential for Contamination . ....................175

FiguresFigure Page

8-1. Environmental impacts of Copper Production . .......................1618-2. Gas Cleaning in Copper Smelting . . . . . . . . . . . . . . . . . . . . . .............1658-3. Copper Converter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......1678-4. Air Curtain Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1698-5. Cost of S02 Removal With an Acid Plant . ...........................1718-6. Sulfur Dioxide Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............1728-7. Wasteland Management Practices . . . . . . . . . . . . . . . . . . . . . . . ..........176

TablesTable Page8-1.8-28-3.8-4

1980 Sulfur Dioxide Emissions in the United States . . . . . . . . . . ..........162State and Federal Primary Ambient SO 2 Standards . ...................163Smelting Technology and Associated Emissions . ......................164Effluent Limitationson Discharges From Mines, Mills, andLeach Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................172

Chapter 8

Environmental Aspects ofCopper Production

Copper production is not an environmentallybenign activity. From mining and milling throughhydro- and pyrometallurgical processing to refin-ing, copper production can have significant ad-verse impacts on air quality, surface and ground-water quality, and the land (see figure 8-1 ). Whilethese impacts can be severe when the materialshandled include toxic or hazardous substances(e.g., ores with a relatively high concentration ofarsenic), they also can be modest due to techno-logical and other pollution controls, and becauseof mitigating features of the climate, geology, andecology of most copper-producing areas in theUnited States.

As with all other industrial activities in theUnited States, copper production is subject toextensive environmental regulation related to airand water quality, and materials handling anddisposal practices. This regulation has had sig-nificant impacts on the mode and cost of do-mestic copper production. For example, sulfurdioxide emission limitations resulted in thereplacement of domestic reverberatory smeltingfurnaces with flash, electric, or continuous fur-naces connected to plants that convert the sul-fur dioxide to sulfuric acid. Operation of the acidplant increases smelter costs. For some domes-tic producers, the sulfuric acid is a salable by-

F i g u r e 8 - 1 . - E n v i r o n m e n t a l I m p a c t s o f C o p p e r P r o d u c t i o n

F u g i t i v ed u s t

Sulfur dioxide,p a r t i c u l a t ee m i s s i o n s AIR

LANDS l i m e s

So l ven tl o s t

Ground wateri n t e r c e p t

L e a c h i n g

WATER

SOURCE: Office of Technology Assessment

161

162

product or usable at a nearby mine for leaching.It also can be a “red ink” item if there are nomarkets within an economical transportationdistance.

Operational changes resulting from environ-mental regulation have conferred significant(but less easily quantifiable) benefits for humanhealth and the environment, but also have hada substantial adverse impact on the competitive-ness of U.S. copper producers. Any tightening

of the present air quality or waste managementrequirements would result in further closures ofdomestic copper operations.

This chapter reviews the environmental aspectsof copper production. It presents a brief overviewof the rationale for regulation, the technologicalcontrols, and the impact of those controls on do-mestic competitiveness. Further analysis of envi-ronmental regulation and its impact on the U.S.copper industry may be found in chapter 10.

AIR QUALITY

Pollutants of Concern andTheir Regulation

Uncontrolled copper smelting processes emitlarge quantities of particulate matter, trace ele-ments, and sulfur oxides, which can have adverseeffects on human health. Sulfur dioxide (SO2),and the sulfates and sulfuric acid aerosols it formsin the atmosphere, can be lung irritants and ag-gravate asthma. Estimates of the magnitude ofhealth risks and the influence of S02 and second-ary pollutants from all emission sources rangefrom O to 50,000 premature deaths per year inthe United States and Canada.1 Sulfur dioxideemissions from smelters also have been linkedto visibility degradation and acid deposition.2 Al-

‘U. S, Congress, Office of Technology Assessment, Acid Rain andTransported Air Pollutants: Imp//cations for Public Policy, OTA-O-204 (Washlngton, DC, U.S. Government Printing Office, June 1984),

p. 13.

‘Robert A. Eldred et al, “Sulfate levels in the Southwest duringthe 1980 Copper Strike, ” Journal of Air Pollution Control, vol. 33,

.

though fossil-fueled electric powerplants are themajor source of S02 emissions in the UnitedStates, smelters contribute significantly to totalemissions in the sparsely popuIated copper-pro-ducing areas of the West (see table 8-l).

Fugitive emissions from furnaces and convert-ers can cause health problems in the work placeand/or result in elevated levels of toxic pollutantssuch as lead and arsenic in the immediate vicinityof the smelter. Generally, employees are exposedto the highest concentrations of toxic elementsbecause they work in enclosed areas. However,

No. 2, 1983; John Trijonis, “Visibility in the Southwest–An Explo-ration of the Historical Data Base, ” Atmospheric Environment, vol.13, 1979, pp. 833-843, and sources cited therein; see also RobertYuhnke and Michael Oppenheimer, Safeguarding Acid SensitiveWaters in the intermountain West, Environmental Defense Fund,November 1984; see also “Acid Deposition in the Western UnitedStates, ” Science, July 4, 1986, pp. 10-14.

) Fugitive emissions are those that escape capture by normaI airpollution control equipment,

Table 8-1 .—1980 Sulfur Dioxide Emissions in the United States(million metric tonnes)

National East West

Source Tons Percent Tons Percent Tons PercentElectric utilities. . . . . . . . . . . . . 15.8 65.6 14.6 73.5 1.2 28.6Nonferrous smeltersa. . . . . . . . 1.4 5.8 0.2 0.8 1.2 29.0Transportation . . . . . . . . . . . . . . 0.8 3,3 0.5 2.5 0.3 7.3Other . . . . . . . . . . . . . . . . . . . . . 6.1 25.3 4.6 23.2 1.5 35.1

Total c . . . . . . . . . . . . . . . . . . . 24.1 100.0 19.8 100.0 4.3 100.0alncludes 28 nonferrous smelters, of which 27 were operating in 1980. Sixteen of the 28 are copper smelters—13 are in the

West. Eight of the copper smelters are still in operationblndustrial, commercial, and residential sourcescTotals may not add due to rounding

SOURCE U S Congress, General Accounting Office, Air Pollution Sulfur Dioxide Emissions from Nonferrous Smelters HaveBeen Reduced, report to the Chairman, Subcommittee on Oversight and Investigations, Committee on Energy andCommerce, House of Representatives, GAO/RCED-86-91, April 1986.

contamination of the soil surrounding a smelteralso is of concern. Fortunately, toxic metals arepresent only in very small concentrations in mostdomestic copper ores.4 Only Asarco’s El Pasosmelter currently treats concentrates that are con-sidered to have high levels of volatile impurities. sThe Anaconda-Butte and Asarco-Tacoma smeltersused to treat such concentrates, but they closedin 1980 and 1985, respectively,

The Clean Air Act established National AmbientAir Quality Standards for six pollutants (see ta-ble 8-2). The Act requires that these standards bemet throughout the United States, including theimprovement of air quality in “dirty” areas andthe prevention of significant deterioration of airquality in “clean” areas. These goals are achievedthrough emission limitations on various types ofsources (including non-ferrous smelters) that re-quire the use of technology-based controls. TheAct also regulates emissions of hazardous pollut-ants. Substantial financial penalties are imposedfor non-compliance.

— — —4State of Arizona, Bureau of Air Quality Control, ThIrd Annual

Report on Arizona Copper Smelter Air Pollution Control Technol-ogy, April 1979.

5A “high Ievel of volatile impurities ” means a total smelter chargecontaining more than 0.2 percent arsenic by weight, 0.1 percentantimony, 4.5 percent lead, or 5.5 percent zinc, on a dry basis.Code of Federal Regulations, Title 40, Part 60.161. July 1, 1986.

Table 8-2.—State and Federal PrimaryAmbient S02 Standards

Federal . . . . . . . . . . . . . . . . 0.03 ppm annual average0.14 ppma 24-hour average0.50 ppma 3-hour average

Arizona . . . . . . . . . . . . . . . . 0.03 ppm annual average0,14 ppm 24-hour average0,50 ppm 3-hour average

Montana . . . . . . . . . . . . . . . 0.02 ppm annual average0.10 ppmb 24-hour average0.05 ppmc 3-hour average

New Mexico . . . . . . . . . . . . 0.02 ppm annual average0,10 ppm 24-hour average

Utah . . . . . . . . . . . . . . . . . . . 0.03 ppm annual average0.14 ppm 24-hour average0.50 ppm 3-hour average

KEY: 1 ppm SO, = 2620 ~glm]ppm = parts per million~g/m] = micrograms per cubic meter.

NOTE The 3-hour average is an annual geometric mean, to be used in assessmentof plans to achieve the 24-hour standard

aNo more than 1 violation/yearbNo more than 2 violations/yearCNo more than 19 violations/year

SOURCE Federal Code of Regulations, Title 40, Part 57102, July 7 1986

163

Smelter Pollution Control

All stages of pyrometallurgical processing emitgases of varying content and volume (see table8-3). Most technological methods of control in-volve collecting the gases and converting the SO2

to some other product. The characteristics of thegases dictate the type of control technology,which in turn determines the kind of byproductsproduced. For example, acid plants–the mostwidely used control technology —require a rela-tively high (at least 4 percent) SO2 concentrationin the off-gas for economical operation and com-pliance with pollution limitations. Roasters, flashfurnaces, electric furnaces, continuous smeltingfurnaces, and converters all produce gases thatcan be treated in an acid plant. Weak gases, suchas those from reverberatory furnaces and fugitiveemissions, must be treated by alternate means. b

Strong Sulfur Dioxide Emissions

Acid plants (figure 8-2) convert the sulfur di-oxide in emissions to sulfuric acid (H2SO4). Otherconversions, including to gypsum, elemental sul-fur, and liquid SO2 are technologically feasible,but usually not economically viable (see box 8-A).

In making sulfuric acid, the hot gases are firstcollected from the roasters, furnaces, and con-verters (see box 8-B). The gases are cooled, cleaned(through three series of dust collection systems)to recover copper from the dust and prevent foul-ing of the acid plant, and then treated with sul-furic acid to remove any water vapor. Catalystsconvert the SO2 gas to sulfur trioxide (SO3), whichis absorbed in a circulating stream of 98.5 per-cent sulfuric acid and 1.5 percent water, andreacts with the water to form more concentratedacid.

There are two basic types of acid plants. In sin-gle contact/single absorption (SC/SA) plants, thegas goes through the system once; such plantsaverage conversion (SO2 to H2S04) efficienciesof 96 to 98 percent. Double contact/double ab-sorption (De/DA) plants maximize S02 capture

b I n the conient 10 na I roast I ng- re~erberatory smelt I rig-co ni e rt I ng~eq ue n c e, f) n [y 50-70 per( c’nt ot the S(IJ prod uceci by the \ me herc an be ca~)( u red I\It h a n a( Id I)la nt.

164

Table 8-3.—Smelting Technology and Associated Emissions

Off gasesTechnology (% S O2 by volume) Fugitive emissions

Multihearth roaster . . . . . . . . . . . .Fluid bed roaster . . . . . . . . . . . . . .

Reverberatory furnace . . . . . . . . . .

Pierce-Smith converter:during blowing . . . . . . . . . . . . . .during charging (change

due to dilution with air) . . . .

Continuous smelting:Noranda process . . . . . . . . . . . .Mitsubishi process . . . . . . . . . .

Electric furnace . . . . . . . . . . . . . . .

5-1o10-12

0.5-2.5

15-21

1-7

16-2011

5 +

Leakage through the shell and open ports and during the filling ofthe transfer car (to transport matte to the furnace).

Emissions escape through openings in the brickwork, duringcharging of calcine or green concentrate, during addition ofconverter slag, at slag and matte launders during tapping, at uptakeand waste heat boilers.

Emissions escape through the primary hooding system and areemitted directly from the mouth of the converter during chargingand pouring.

Noranda emissions from between the primary uptake hood andfurnace mouth, from the mouth when in the rolled out position,around matte tapping, and at the port for feeding concentrates andfluxes.

Fugitive emissions lower than most reverberatories; if not properly

Flash smelting:30°/0 oxygen enriched . . . . . . . . 10-20tonnage oxygen . . . . . . . . . . . . . 70-80

Hoboken Converter . . . . . . . . . . . . 8-9

maintained, brickwork could be a source of emissions. Emissionsmay occur during slagging, matte tapping, converter slag return,around the electrodes, and the calcine handling.

Fugitive emissions at launders and ladles and from leakage throughthe furnace walls and roof.

This converter has no primary hood, so any emissions from themouth of the converter are fugitive emissions; properly designed,operated, and maintained, there are minimal fugitive emissions.Fugitive emissions occur during the hot metal matte charging orhot blister metal pouring.

SOURCE: Timothy W, Devitt, Control of Copper Smelter Fugitive Emissions, PEDCo-Environmental, Inc , May 1980, p, 14

by returning the gas stream to the convertersthrough an intermediate absorption tower. Theseplants are capable of 99.7 to 99.8 percent con-version efficiencies.7

The design of an acid plant is unique to eachsmelter. The key variables affecting the efficiencyand economics of acid production are the totalgas volume; and the SO2 concentration, watervapor concentration, and free oxygen content ofthe treated gases. The physical dimensions andenergy requirements of the acid plant are largelydetermined by the maximum volume and mini-mum concentration of SO2 gas.8

There are several reasons why acid plants areso widely used by the U.S. copper industry. Thetechnology is well proven and is the least expen-

7Charles H. Pitt and MiIton E. Wadsworth, A n Assessment ofEnergy Requirements in Proven and New Copper Processes, re-port prepared for the U.S. Department of Energy, contract no. EM-78-S-07-1 743, December 1980.

‘1 bid.

sive method of smelter SO2 control. Sulfuric acidis used in solution mining, and also is the mostcommon form in which other industries consumesulfur; thus it can be a salable byproduct ratherthan a waste. However, non-leaching markets forsulfuric acid generally are a long way from thesmelters in the United States, and the resultingtransportation costs can turn the byproduct creditinto a deficit. Moreover, it often is cheaper forindustrial consumers to buy sulfur and producethe sulfuric acid themselves than to purchase acidproduced elsewhere.9

In some countries, such as Japan, a very highlevel of SO2 control is achieved by copper smeltersas part of a government policy to provide sulfuricacid for industrial development (see ch. 4). In lessdeveloped areas, such as the copper-producingcountries of Africa and Latin America, there are

9Michael Rieber, Smelter Emissions Controls, The Impact on Min-ing and the Market for Acid, prepared for U.S. Department of theInterior, Bureau of Mines, March 1982.

165

Figure 8-2.-Gas Cleaning in Copper SmeltingSmelter

Roaster o f f g a s Converteroff g as off g as

Gas cooler Dust recycledto smelter

Hot ESPDust recycled

to smelter

To stack ‘ 1 J

I

To stack ,

Scrubber Sludge todisposal

III

Stream Legend[

Gas

I

Cleaned g a sto acid plant

SOURCE” Charles H. Pitt and Milton E. Wadsworth, An Assessment of Energy Requirernents in Proven and New Copper Process.es, report prepared for the U.S. Department of Energy, contract EM 78. S-07-1 743 Dec. 31, 1980

Box 8-A.—Alternative Byproducts From the Control of Strong S02 Emissions

Elemental Sulfur. The reduction of sulfur dioxide to elemental sulfur is technically complex and re-quires an extremely high concentration of S02 in the off gases. Therefore, elemental sulfur productionis feasible only with the INCO flash furnace, which uses tonnage oxygen (rather than oxygen-enrichedair) and has emissions of up to 75 to 80 percent S02. This conversion also requires large amounts of hydro-carbon fuel, such as coke, which reacts chemically with the S02 to form elemental sulfur. The fuel is rela-tively expensive and more than triples the energy requirement of the S02 control system.l However, elemen-tal sulfur can be transported economically much greater distances than either sulfuric acid or liquid sulfurdioxide, and is more easily stored when demand is low.

Liquid Sulfur Dioxide. Liquid sulfur dioxide production also works best with a highly concentratedgas stream like that emitted by the INCO furnace. Liquid S02 has a very limited demand in the UnitedStates, but, owing to its relatively high price per unit weight, it can be shipped long distances. It is stillextremely expensive to transport, however, because it requires special pressurized tank cars that usuallyreturn empty. The market is too small to justify cost saving measures such as unit trains or special oceantankers. 2

‘ D ,1 5( h LJ 11/ ‘ P O Iutlon Control .]nd Enerp,\ Con~umptlon .]t U S. Copper S m e l t e r s , /ourn’]1 of MefJl$, Ianuar} 1 9 7 8 , p .?0.-’NIIc h,](,l Rit,l)er $mf,lter En~IssIon\ Corrfrol, The lmp,i[ t on \fjnlng ,Ind the if,]rkef for 4c-d prep.ired tor U S Department ot the Interior Bu rt>,~u

(N ,\l I nt,< ,i!a r( h 1982.

166

Photo credit: Robert Niblock

Acid plants entail extensive gas collection systems.

few industrial markets for acid, and SO2 controlis minimal (see figure 8-6, below).

It is important to note that not all of the SO2

produced in a smelter is processed in the acidplant, Some of the sulfur dioxide gas is too weakto treat in the acid plant and some escapes as fu-gitive emissions. Gases from the acid plant itselfcontain unreacted sulfur dioxide and unabsorbedsulfur trioxide and usually are treated to removeacid mist before being vented to the atmosphere.

Weak Sulfur Dioxide Emissions

Weak gas streams, with an SO2 concentrationof less than 4 percent by volume, constitute amore difficuIt and costly problem than strongerstreams. These include both smelter gases andfugitive emissions. For smelters, the three avail-able control options are flue gas desuIfurization,

modifying the furnace to produce stronger gasstreams, and replacing the equipment with newertechnology. All but two of the operating domes-tic smelters chose the third option.

In flue gas desulfurization (FGD), the SO2 ischemically removed through reactions with lime,magnesium oxide, ammonia, or dimethylaniline(DMA, an organic liquid). Regenerative FGD sys-tems upgrade the sulfur dioxide content of thegases so that they may be further treated in anacid plant. Non regenerative systems result in awaste product (scrubber sludge). Although FGDis a well proven technology in fossil-fueled pow-erplants, and the Environmental Protection Agency(EPA) considers it adequately demonstrated innonferrous smelters, very few smelters have ac-tually installed scrubbers.10 In early trials, smeltersexperienced frequent scaling and plugging prob-lems with scrubbers. Phelps Dodge installed anexperimental DMA system at their Ajo, Arizonasmelter; it was operated intermittently and is nolonger in use.11 Currently, the White Pine, Mich-igan smelter is using gas scrubbers without anacid plant, and is in compliance with emissionIimitations. 12

A broad range of reverberatory furnace modifi-cations are available. The furnace can be sealedtightly to prevent infiltration of air and the sub-sequent dilution of the gases. oxygen-enrichedsmelting can increase the S02 content of the offgases while it reduces the overall volume of gas.Weak or intermittent gas streams can be blendedwith stronger gas streams to produce a streamamenable to S02 control. Supplemental sulfurcan be burned in conjunction with a sulfuric acidplant to generate a supply of sulfur dioxide thatcan be used to beef up weaker gas streams.

Finally, reverberatory furnaces can be replacedwith newer technology, resulting in the greatestimprovements in sulfur capture. Although a com-plete smelter retrofit involves large capital costs

IOA v slack, “AppllCatjOn of Flue Gas Desulfu rization in the Non-

ferrous Metal Industry, ” Sulfur Dioxide Control in Pyrometallurgy,The Metallurgical Society of AlME, Chicago, Illinois, February 1981,p. 92.

I I Pitt and Wadsworth, supra note 7.l~)anlce l., W. Jolly and Daniel Edelstein, “Copper,” preprint from

1986 Bureau of Mines Minerals Yearbook (Washington, DC: U.S.Department of the Interior, 1987).

167

(see ch. 9), the newer furnaces comply more eas-iIy with air quality standards and are more effi-cient. Another alternative involves replacing oraugmenting smelting with hydrometallurgicalprocesses. Leaching and solvent extraction do notproduce sulfur dioxide gas, but they can fall un-der water quality and waste disposal regulation.Moreover, only oxide ores and oxidized wastematerial currently can be leached economically.

The Pierce-Smith converter is the major sourceof fugitive emissions in a smelter building. Fugi-tives are emitted directly when the converter isrolled for the addition of matte (figure 8-3). Theyescape the primary hood (box 8-B) when it ismoved to provide clearance for the overheadcrane and matte ladle. Significant amounts ofgases also escape from the hood during air in-jection (blowing). Moreover, the fan in the hoodshuts down during charging, but, before the con-verter has completely rolled back to the verticalposition and the hood and fan are fully opera-tional, blowing resumes, allowing fugitives to es-cape. 13

I ~Ti mOth y \${, Deklrr, control ot’ Copper Srne/ter FU<qItIL’~ Em Is-

sIon\, PEDCo-Environ mental, Inc., May 1980, p. 14.

Figure 8-3.—Copper Converter Operation

\Primary

hood

Photo credit: Manley Prim Photography, Tucson. AZ

Skimming from a converter.

Charging Blowing SkimmingSOURCE: John O. Burckle et al , Evaluation of an Air Curtain Hooding System for a Primary Copper Converter, Vol. 1, Prepared for U S Environmental Protect Ion

Agency, Industrial Environmental Research Laboratory, by PEDCo Environmental, Inc., February 1984

168

Box 8-B.—Collecting Converter Gases

Converter gas streams are more difficult to col-lect than those from roasters and smelters. Ahood is lowered to the converter mouth to cap-ture the gases and particulate matter that areemitted while air is being blown into the matte.The primary hooding system on most convertersconsists of a fixed hood with a sliding gate lo-cated above and slightly away from the convert-er (see figure 8-3). During blowing, the gate islowered to the converter mouth to help guidethe emissions and reduce the intake of cool am-bient air.

Primary hoods are not 100 percent efficientbecause the gate does not form a perfectly tightseal with the converter mouth. At plants wherethe gates were retrofitted rather than designedand installed as part of the original smelter, thegate often does not completely cover the con-verter mouth. Contact with the crane and ladlesalso can damage the hooding system, and pre-ventive maintenance is required to repair leaksdue to normal wear and tear.

A secondary hood that slips over the primaryhood affords some additional emissions captureduring the critical times of charging and skim-ming. Double hood systems have exhibited op-erational problems, however. They can becomewarped to the point that they no longer fit overthe primary hood, and at times they do not sup-ply enough draft or are too far from the mouthof the converter to be effective. }

‘Carl H. Billings, Secortd Annual Report on Arizona Copper SmelterA/r Pollutlon Control Technology, State of Arizona, Bureau of AirQuality Control, April 1978, p 40

Methods of capturing fugitive emissions fromconverters include secondary hoods, air curtains,ventilation systems, and alternative convertertechnologies. Air curtains use a row of nozzlesto create a stream of air that captures around 90percent of the gaseous emissions and particulateover the converter (see figure 8-4). ’4 As with pri-mary hoods, however, contact with cranes and

I qjohn 0, gu rckle, et al., Evacuation of an Air Curtain Hood;ng

System for a Primary Copper Co~verter, Volume It Prepared forU.S. Environmental ProtectIon Agency, Industrial EnvironmentalResearch Laboratory, by PEDCo Environmental Inc., February 1984,p. 4.

ladles can damage or misalign air curtains. Thissort of technology could be effective at fugitiveemissions control if design changes could makeit more adaptable to the smelter environment.

Another option for fugitive emissions controlis a total building ventilation and collection sys-tem. Such a system did prevent high ambient airreadings at monitoring stations around one smelterin which it was tried, but created dead spots in-side the building where there were increasedconcentrations of SO2 and elevated temperatures,largely due to inadequate fan capacity. Total ven-tilation may also create heating problems duringcold spells as most of the heat is evacuated withthe emissions.15

Alternative converter technologies include con-tinuous reactors and the Hoboken converter.Continuous reactors theoretically combine roast-ing, smelting, and converting in one operation.In the Mitsubishi continuous reactor, the con-verter portion is enclosed and the potential forfugitives should be reduced substantially. TheNoranda reactor both has a hood and typicallyis used in conjunction with a Pierce-Smith con-verter (see ch. 6).

Inspiration Consolidated Copper Company(ICCC) experimented with an induced draftHoboken Converter, which was supposed to con-trol emissions by maintaining a negative draft atthe mouth at all times. Concentrations of 8 to 9percent SO2 were achieved in early tests–suffi-cient for treatment in an acid plant. Subsequently,however, ICCC experienced operational prob-lems, fugitive emissions became progressivelyworse, and they replaced the converter. 16

Costs and Benefits ofPollution Control

Control strategies have resulted in marked im-provements in long term SO2 levels in the past15 years, with substantial benefits for publichealth and the environment. According to EPAstatistics, copper smelters reduced their total sul-

I ~carl H. Bl[lings, Ttr;rci Arrrrua/ Report on Arizona Copper smelter

Air Po//ut)on Contro/ Technology, Arizona Bureau of Air QualityControl, April 1979, p. 42.

161bid.

169

Figure 8-4.-Air Curtain Control System

Jet side Exhaust side

Aircurtain

jet

B a f f I ewaI I

Air curtain- - - - - - - - - ----------------------------- .- . . .- -. ---

------- .-

BaffIewalI

To suet ion fan andh o o d s a m p l e l o c a t i o n

SOURCE John O Burckle et al., Evaluation of an Air Curtain Flooding System for a Primary Copper Converter, vol. 1, report prepared for U S. Environmental ProtectionAgency, Industrial Environmental Research Laboratory, by PEDCo Environmental, Inc., February 1984.

fur dioxide emissions from 3.5 million tons in1970 to 970,000 tons in 1983—a 72 percent re-duction. The percent of input sulfur captured atdomestic smelters is currently 90 percent.17

These gains were not easy. By the very natureof their operation, smelter and converter emis-sions are difficult-and expensive—to capture andcontrol. Before technological means of controlbecame mandatory, smelters used supplemen-tal and intermittent SO2 controls. 18 While these

17Duane Chapman, “The Economic Significance of Pollution Con-trol and Worker Safety Costs For World Copper Trade, ” CornellAgricultural Economics Staff Paper, Cornell Universityr Ithaca, NewYork, 1987.

18Supplemental control systems Include the use of very tall stacksto disperse pollutants, thus diluting their ambient concentration.Intermittent control consists of monitoring the ambient weather con-ditions to identify when wind patterns and termperature inversionscould trap the pollutants near the source instead of dispersing theplume. Under these conditions, production is cut back to the pointnecessary to reduce pollutant emissions to an acceptable ambientconcentration,

methods resulted in lower overall SO2 emissions,they also reduced production .19 When smeltershad to install technological controls, many closedbecause the capital cost of retrofitting the smelterwas too high. The General Accounting Office esti-mates that between 1970 and 1984, 44 percentof the reduced emissions from non-ferrous smelters(including lead and zinc operations) were due toimprovements in control techniques, while 56percent were due to decreased production .20(Smelters that closed during 1984 and 1985 hadbeen responsible for over half of NAAQS vio-lations.)

Although the need to replace reverb with

other furnaces plus pollution control devices

19Rieber, supra note 9.20

U .S . Congress, GeneraI Accounting Office, Air Pollution, Sul-

phur Dioxide Emissions From Nonferrous Smelters Have Been Re-duced, April 1986, p.4.

170

brought social benefits and increased furnaceefficiency, it also cost the domestic industry anenormous amount of money and contributedto the closure of significant domestic capacity.The primary copper industry had capital invest-ments totalling $2.088 billion for air pollutioncontrol between 1970 and 1981, with average an-nual costs of $3.074 billion .21 Furthermore, add-ing an acid plant to the production line increasesoperating costs without necessarily providing abyproduct credit. Present levels of control entailcapital and operating costs of between 10 and15 cents per pound of copper.22

The capital cost of sulfur removal, which in-cludes gas handling of a 4 percent sulfur dioxidegas stream and the sulfuric acid plant at a 50,000tonne per year copper facility, has been estimatedat $560 per annual tonne of copper produced.23

This is approximately 20 percent of the total cap-ital costs of the facility. Both the capital invest-ment and the operating cost for S02 removal de-crease with increasing concentration of SO2 in——

21 Lawrence J. McDonnell, “Government Mandated Costs: The

Regulatory Burden of Environmental, Health, and Safety Standardsof U.S. Metals Production, ” paper prepared for the conference Pub-lic Policy and the Competitiveness of the U.S. and Canadian Me-tals Production, Golden, CO, January 1987.

22Everest Consulting, Air Pollution Requirements for CopperSmelters in the United States Compared to Chile, Peru, Mexico,Zaire and Zambla, 1985.

23Jadgish C. Agarwal and Michael J. Loreth, ‘‘ Preliminary Eco-

nomic Analysis of S0 2 Abatement Techno log ies , : Su l fu r D iox ideControl in Pyrometallurgy, The Metallurgical Society of Al ME, Feb-ruary 1981.

the gas stream because of lower costs associatedwith handling a smaller gas volume (see figure8-5). Fugitive emissions are the most difficult andexpensive to control because they are dilute,have a large volume, and are not easy to capture.

In comparison, copper smelters in Chile, Can-ada, Peru, Mexico, Zaire, Zambia and Japan—our major foreign competitors—are not facedwith similar environmental regulations. I n all butJapan, if smelter emissions are controlled at all,it is only to the extent that sulfuric acid is neededat an associated leaching project. Copper smeltersin these countries capture between O and 35 “per-cent of the input sulfur; on average only aboutone-fifth of the present level of U.S. control (seefigure 8-6). Japanese smelters achieve 95 percentcontrol as part of government policy to subsidizesulfuric acid production. Information regardingthe costs of acid production in these countriesis not available.24 However, it is clear that domes-tic regulation puts U.S. producers at a competi-tive disadvantage.

Future capital investments in Chile, Peru, Mex-ico, Zaire, Zambia may be funded in part by theWorld Bank (see ch. 3). The World Bank requiresenvironmental controls as a condition for financ-ing, but they are less stringent than Clean Air Actstandards, and compliance is not monitored .25

24MacDonnell, supra note 21.25Everest Consulting, supra note 22.

WATER QUALITY AND WASTE DISPOSAL

All aspects of copper production—from min-ing and leaching to milling, smelting, refining andelectrowinning—have potential impacts on sur-face and groundwater quality (see figure 8-1).26

Adverse water quality impacts are caused primar-ily by land disposal practices that fail to containwastes, by run-on and run-off controls that areinadequate to prevent surface water from flow-

26surface waters include the various terms of water occurring onthe surface of the earth, such as streams, rivers, ponds, lakes, etc.Groundwater is water that flows or seeps downward, saturating soilor rock and supplylng springs or wells. The upper level of this satu-rated zone is called the water table. Aquifers are underground watersources large enough to be used for public water supplies.

ing through impoundments, or by groundwaterinfiltrating surface impoundments.27 In addition,the large-scale land disturbances associated withopen-pit mining may disrupt the natural flow ofsurface and groundwaters, and may lower thewater table in the mine area. Lowering the watertable may cause water shortages, land subsi-dence, and fracturing; the latter facilitates thetransport of contaminants into and through anaquifer.

. — — —27SCS Engineers, Summary of Damage Sites from the Disposal of

Mining Wastes, prepared for the U.S. Environmental ProtectionAgency, January 1984.

1000

100

10

1

0 1

Figure

171

8-5.-Cost of S02 Removal with anAcid PIant

miIlions of 1980 dollars

1 I I I I I I I

10000S 02 input rate (1bs/hr )

Operating cost, millions of 1980 dolIars

T“

.

2% S02

I 1 1 It

10000 100000 1000000S 02 Input rate (lbs/hr)

SOURCE: Jadgish C Agarwal and Michael J. Loreth, “Preliminary Economic Analysis of SO2 Abatement Technologies,” SulfurDioxide Control in Pyrornetallurgy, The Metallurgical Society of AlME, February 1981

172

Figure 8-6.-Sulfur Dioxide Control

AUs t r al I a

Canada

Chile

Japan

Peru

PhiIippines

U.S.

Zaire

Zambia

I I I I I I

1200 800 400 0 25 5 0 75 1001000 tonnes smelter product ion % sulfur control

SOURCE Duane Chapman, “The Economic Significance of Pollution Control and Worker Safety Costs for World Copper Trade,”Cornell Agricultural Economics Staff Paper, Cornell University, Ithaca, New York, 1987.

The EPA administers four major legislative pro-grams that could affect water quality control andwaste disposal practices at domestic copper min-ing operations: 1 ) the Clean Water Act, which im-poses effluent limitations on point sources (seetable 8-4) and requires permits for the dischargeof any effluent u rider the National PolIution Dis-charge Elimination System (NPDES); 2) the Re-source Conservation and Recovery Act (RCRA),which regulates the generation, transport, anddisposal of hazardous and solid wastes (see box8-C); 3) Superfund, which assigns priorities for,and oversees the cleanup of, polluted sites; and4) the Safe Drinking Water Act, which is designedto protect the quality of public drinking watersupplies. In addition, new or substantially modi-fied copper operations are subject to the NationalEnvironmental Policy Act of 1969 (N EPA), whichrequires Federal agencies to prepare an environ-mental impact statement (EIS) for any major Fed-eral action (e.g., issuing a permit) that will sign if-

Table 8-4.—Effluent Limitations on Dischargesfrom Mines, Mills, and Leach Operationsa

Effluent limitations (mg/l)

Average of dailyEffluent Maximum for values for 30characteristic any one day consecutive days

TSS . . . . . . . . . . . . 30.00 20.00Cu . . . . . . . . . . . . . 0.30 0.15Zn. . . . . . . . . . . . . . 1.50 0.75Pb . . . . . . . . . . . . . 0.60 0.30Hg . . . . . . . . . . . . . 0.002 0,001pH . . . . . . . . . . . . . 6.0-9.0 6.0-9.0Cd . . . . . . . . . . . . . 0.10 0.05aLeaching Operations are expected to achieve zero discharge unless the annual

precipitation exceeds the annual evaporation, in which case a volume of waterequal to the amount exceeding annual evaporation may be discharged subjectto NPDES limitations

SOURCE: Ore Mining and Dressing Point Source Category Waler Pollution Ef-fluent Guidelines, 40 CFR Ch.1 (7.1-85 edition)

icantly affect the environment. Tailings dams alsoare subject to Federal design standards to ensurepublic safety.

Although water quality control and wastemanagement have not yet had the same finan-

173

BOX 8-C. —The Resource Conservation and Recovery Act

Future regulation of mine wastes under the Resource Conservation and Recovery Act (RCRA) is ofmajor concern to the domestic copper industry. Subtitle C of RCRA governs hazardous wastes, while s u b -title D provides guidelines for non-hazardous solid and liquid wastes. In 1986, EPA decided that solid wastesfrom the mining and beneficiation of copper ores should not be regulated under Subtitle C of RCRA ashazardous, even though copper dump leach liquor, copper dump leach wastes, and tailings may exhibithazardous characteristics of corrosiveness or Extraction Procedure (EP) toxicity.1 The rationale for this de-cision was that the large volumes of mine waste would be very difficult to regulate under rules designedto manage much smaller amounts of industrial and municipal waste. Also, EPA reasoned that Subtitle Cdoes not allow considerations of environmental necessity, technological feasibility, and economic practi-cality, which are important given the magnitude of mine waste. z

The cost of mine waste management under Subtitle C of RCRA would result in further closures of do-mestic mines and mills. EPA believes that concerns about actual and potential releases of hazardous con-taminants from mine wastes can be addressed adequately by designing a regulatory program specific tosuch wastes under the more flexible Subtitle D solid waste management authority. Subtitle D gives EPAthe authority to set waste management standards intended to protect surface and groundwater qualityand ambient air quality. At the same time, it allows consideration of the varying geologic, hydrologic, cli-matic, popuIation and other circumstances u rider which different waste management practices assure rea-sonable environmental protection.3

Critics of this approach argue that Subtitle D regulations do not fully address mine waste concerns,especially for hazardous wastes. In addition, based on information supplied largely by the mining indus-try, EPA is uncertain whether current waste management practices can prevent damage from seepage orsudden Ieaks.4

‘ The E P tox Ic Ity test I> an a nalyllcal techn Iq ue used by EPA to predict the leaching potentla I of wastes1~1 f E n \ lronment~l Prot[,ctlon Ag[,nc} (EPA), II asfes from the f,xfra(-tlon and f?erreflclafion o f Meta//tc ores Pho~ph,ite R(x k, A\shestof [)L erhur-

d~’n Iron] ~r,]nlurn \IImrJg and Oil Shale, Report to Congres\, December 1985, p. ES-13.I Non-(-(ja I M I n I ng LVa\te< To Be Regu Iated U ncier RCRA, But Not A\ Hazardous, EPA Says, ’ Em fronrnenf R e p o r t e r , July 4, 198(,, p p 155-35(>.

‘Rcgu I.it(jr\ Dt>term I nat Ion for k%’~ste> from the Ext rac tlon a nri Benet[clat[on ot’ Ore\ and IMI nerals, Federal Register, Iuly 3, 1986

cial or capacity impact on the domestic copper waste. The EPA estimates that, between 1910 andindustry as air pollution control, their costs arenot insignificant. The U.S. nonferrous ore min-ing and dressing sector had a total capital invest-ment of $667 million in water pollution controlbetween 1970 and 1981, with average annualcosts of $708 million .28 Copper operations han-dle much larger amounts of material than othermetal mining industries and generate consider-ably more solid waste, and a large share of thiscost can be assigned to the domestic copperindustry—perhaps as much as half. Data on for-eign water pollution control practices were notavailable.

Pollutants of Concern

The mining and beneficiation of copper oreproduces enormous volumes of liquid and solid

1981, all types of metallic ore mining and benefic-iation in the United States generated a cumula-tive total amount of waste of more than 40 bil-lion tonnes. Copper production accounts forroughly half of this total. In 1980, when U.S. cop-per mine production was 1 million tonnes, thedomestic industry generated an estimated 282million tonnes of mine waste, 241 million tonnesof tailings, and 200 million tonnes dump leachwastes .29

Most of the copper mined in the United Statescomes from sulfide ores such as chalcopyrite andbornite–mineral compounds characterized bythe linkage of sulfur with the metal(s) (see ch. 5).

“U. S. Environmental Protection Agency (EPA), Wastes from theExtraction and Beneficiation of Metallic Ores, Phosphate Rock, As-bestos, Overburden from Uranium Mining, and Oil Shale, Reportto Congress, December 1985, p. ES-13.

174

Mining exposes the sulfides to water and air,causing a reaction that forms sulfuric acid andiron. The acidic effluents can dissolve and trans-port heavy and toxic metals from the solid wasteor surrounding ground. Arsenic, lead, and cad-mium are the metals of concern most commonlyassociated with copper ores. These toxic metalscan accumulate in the environment and concen-trate in the food chain, reaching levels that aretoxic to both human and aquatic life. Removaland fracturing of rock and soil during mining alsospeeds up normal weathering processes and in-creases the load of sediments and fine solidstransported by wind and water.

The EPA conducted a study to determine whethermine waste facilities leak and, if they do, whetherthey release contaminants of concern in signifi-cant quantities. Surface and groundwaters weremonitored at eight active metal mine sites. Re-sults indicated that constituents from impound-ments do enter groundwater at most sites, butsignificant increases in concentrations of hazard-ous constituents were rarely demonstrated. so

On the other hand, court cases show that run-off and seepage have caused surface and ground-water contamination at active, inactive, andabandoned mine sites. Much of the damage wascaused by outmoded disposal practices, but therelatively even distribution among the three typesof facility status indicates that the problem is notassociated solely with abandoned or inactivemine sites.31 Some sites may have been active fora long time, however, and while even there theproblematic disposal practices are no longer inuse, their effects may continue.

The potential for contamination of surface andgroundwaters due to the activities of the copperindustry varies widely depending on a variety ofsite-specific factors. The considerations discussedin box 8-D, and the chance that potential prob-lems may not be identified by the current RCRAcharacterizations of wastes, led the EPA to be-lieve that entirely different criteria may moreappropriately identify the mining wastes mostlikely to be of concern.32

1OR~~u latorY Deterrn i nation for Wastes from the Extraction and

Beneficiation of Ores and Minerals, Federal Register, July 3, 1986.II SCS Engineers, supra note 27.~ZFederal Register, supra nOte 30.

Waste Management Practices

In the great majority of cases, potential ad-verse impacts from copper wastes can be con-trolled to acceptable levels with establishedwaste management practices (see figure 8-7).These practices can be summarized in three maincategories: 1 ) minimization, collection, and treat-ment of mine drainage, mill process water, andcontaminated surface drainage; 2) handling, stor-age, and ultimate disposal of tailings and wasterock; and 3) reclamation of the site to minimizelong-term environmental effects once active min-ing has ceased. 33 Waste reprocessing and utili-zation is a fourth method that could offer manyadvantages over disposal, but the enormous vol-umes of waste preclude this from being a viablealternative to disposal.

Collection and Treatment ofLiquid Wastes

Disposal of liquid wastes is rarely a problemas most water can be treated (if necessary to re-move contaminants that would interfere with itsuse) and recycled for drilling, dust control, orprocess water at the mill. Indeed, such recyclingcan augment water supplies in the arid and semi-arid Southwest. Water containing relatively highconcentrations of soluble metals can be used inthe flotation circuits, which will precipitate themetals. Total suspended solids (including metals)in wastewater are controlled by building sedi-ment control ponds, in which the water is heldlong enough for most of the sediment to settle.Sedimentation ponds must be designed with re-spect to predicted frequency and volume of dis-charge; a series of settling ponds can be used toimprove the entrapment of sediment.

Mine Water.—Water can accumulate in sur-face mines and underground shafts due to hy-draulic backfill operations; groundwater seepageinto the mine; water use for machine operationsincluding drilling, dust suppression, cooling, andair conditioning; sanitation and drinking water;and direct rainfall. Volumes vary widely depend-

J~A]an V. Bel [, ‘‘Waste Controls at Base Metal Mines, .Env;ron-

r-nenta/ Science and Technology, vol. 10, No. 2, February 1976,pp. 130-135.

175

Box 8-D. —Factors Affecting the Potential for Contamination

The Location of the Site.—Sites well removed from urban areas, drinking water supplies, surface waters,and sensitive ecosystems are not likely to pose high risks. Most active U.S. copper operations are in sparselypopulated, arid areas where the transport of contaminants is limited by the scant annual precipitation.

The Climate.–Surface infiltration to groundwater is limited in arid and semiarid regions with little sur-face water. Almost 80 percent of copper sites are located in areas with a net annual recharge of less thantwo inches. ’ However, heavy storms could cause some leaching of the waste and result in acid flushesto the surrounding area.

The Hydrogeology of the Site.—The geologic structure of subsurface and related surface water sys-tems may prevent contamination by effluents. For example, aquifers may be protected from effluents bythick layers of alluvium deposits or an impervious clay cap. EPA studies indicate that 70 percent of allmine waste sites (including copper) have groundwater depths greater than thirty feet, so there is time forthe soil to mitigate any seepage that might occur. Other formations such as bedrock may divert effluents.

The Buffering Capacity of Soil.–Some copper ores in the southwestern United States are embeddedin host rock of sedimentary limestone (calcium carbonate, CaC03, is the chief constituent of Iimestone).As the effluent passes over or through limestone formations, it is partially neutralized, the pH increases,and some of the metals wiII precipitate out of the solution. The buffering capacity of Iimestone degradesover time. Other copper ores are formed in acid igneous deposits in which calcareous mineraIs are rareand acid formation potential is correspondingly high.

Removal Mechanisms in Surface Waters.—Alkalinity is described as the ability of water to neutralizeacid. Bicarbonate (HCO3) and carbonate (CO3

-2) from adjacent limestone and feldspar formations arethe principal sources of alkalinity in most surface waters. Alkalinity also tends to precipitate metals. Condi-tions may arise later that will re-solubilize the metals, however, and they can become a source of lowlevel, nonpoint pollution for years to come. The real extent of the pollution is determined by the volumeand velocity of the receiving waters. As with buffering by soiIs, the alkalinity of surface waters is finite.2

Photo credit Jenifer Robison

The arid climate, low population density, and otherfeatures of the Southwest mitigate the potential forsurface and groundwater impacts from copper mining.

ing on mining methods, the climate, and thehydrogeological characteristics of the region. 34

Excess water usually is stored in natural drainageareas or in surface impoundments where it evap-orates or is later used as process water.

Mill Process Water.–Water use in froth flota-tion is high (in Arizona, about 126,000 gallonsper ton of copper produced); around 80 percentis recycled. Occasionally, a buildup of reagentsin the process water will interfere with flotation,and it becomes necessary to discharge and re-place the water. Any discharge is required tomeet effluent Iimitations.

‘~lbld.

176

Figure 8-7.-Wastes and Management Practices

R e c y c l e

N P D E S O t h e r M i nep e r m i t t e d on sited i s c h a r g e u s e

Off siteO n s i t eu s e

u s e

SOURCE: U.S. Environmental Protection Agency, Wastes from the Extraction and Beneficiation of Metallic Ores, Phosphate Rock, Asbestos, Overburden from UraniumMining arid Oil Shale, report to Congress, December 1985,

Smelting and Refining.–Guidelines are beingdeveloped for effluents discharged from primarycopper smelters, electrolytic copper refineries,and metallurgical acid plants. These limitationsaim to control the amount of arsenic, cadmium,

copper, lead, zinc, and nickel in effluents; thepH of the discharge; and the concentration of to-tal suspended solids. Treatment of wastewaterfrom these sources is similar to that describedabove for mines and mills.

Leachate.–The seepage and leaking of sulfuricacid solutions could contaminate both surfaceand groundwater. However, this potential is off-set by the miner’s interest to collect as much ofthe copper-bearing Ieachate as possible. Leachatecollection systems include hydraulic draws thatexploit the natural slopes of the area, sumps lo-cated beneath the heap/dump, or a more sophis-ticated pumping system with secondary Ieachatecollection to control contamination, Older oper-ations generally do not have protective liners, andexperience some loss of Ieachate. New leachingoperations use impermeable membranes to con-fine leach solutions and channel them to a col-lection pond.35

35Stephen F. Walsh, “The San Manuel Oxide Open Pit Project, ”Presented to the Arizona Conference of AlME, Dec. 9, 1985.

177

Handling and Storage of Solid Wastes

As noted previously, solid wastes are generatedduring mining and milling, as well as smelting andconverting. The primary pollution problem is thepotential for sulfide minerals to form sulfuric acid,which in turn is capable of leaching metals fromthe wastes and the surrounding formations andtransporting them to surface and groundwatersystems.

Mine Waste.–Copper mining generates largevolumes of waste rock and dirt, either from thematerial overlying the deposit (overburden), rockremoved from underground mines while sinkingshafts, ore that is too low in grade to be commer-cially valuable, and the rock interbedded with theore body.36 This distinguishes mining from manyother process industries where wastes are a rela-tively small portion of the total materials used toproduce a final product. indeed, larger mineshandle more material and generate more wastethan many entire industries. 37

Although mine waste makes up the largest frac-tion of total solid waste from copper production,it has fewer stability and environmental problemsthan other solid wastes.38 The waste typically isdumped in a pile near the mine site by the truck-

J6U ,s. E P A, supra no te 29 .

~zFederal Register, supra n O t e 30.

MG, W, Center et a 1., De~,elopment of Systematic W’dste D;5P0.$c?I

Plans tor Metal and Nonmetal Mines, Goodson and Associates, Inc.,Aurora, Colorado, Prepared for the Bureau of Mines, June 1982,p. 14.

Photo credit Jenifer Robison

Copper mining generates large volumes ofwaste rock and dirt.

load. This usually produces steep slopes andsome segregation of particle sizes, with the largersizes relegated to the bottom of the coarse ma-terial. There may be some deliberate segregationof the waste to stockpile low grade ore for leach-ing operations.

Leach Waste.–Once leaching is discontinued,the heap/dump becomes leach waste, which canrelease acidic effluents, toxic metals, and total dis-solved solids to the surrounding area. If the leachpile is in a recharge area, groundwater contami-nation could occur. The liners used in new leach-ing dumps continue to provide groundwater pro-tection after closure, but older, unlined dumpsmay degrade surface and groundwater if steps arenot taken to contain or prevent seepage.

Tailings.–Tailings differ from mine and leachwaste in that they are very fine and they retaina certain amount of water after disposal. Fine par-ticle sizes tend to liberate more contained toxicsat a faster rate than coarser wastes. If future ad-vances in processing include grinding ore morefinely to increase metal recovery, tailings disposalwill become even more complicated.

Seasonal or intermittent releases due to heavyrainfall and continuous seepage from ground-water infiltration are the most common mecha-nisms of tailings transport. Seepage can flush sul-fates, dissolved solids, trace metals, and organicsinto groundwater. In older tailings, heavy rainscan oxidize pyritic minerals and form an acidiceffluent that is capable of mobilizing residual me-tals. Arsenic, cadmium, and lead are the toxicsmost frequently released from tailings ponds, al-though other trace metals such as copper, gold,silver, and zinc also may be released .39

Miscellaneous Sludges and Dusts.–In thisgroup of wastes, the sludges generated by sul-fide precipitation (followed by sedimentation) areof greatest concern; EPA believes these will beclassified as hazardous under RCRA, and consid-ers the potential control costs achievable.40 Other

3 9 S C S E n g i n e e r s , s u p r a n o t e 2 7 .40Nonferrous MetaIs Manufacturing Point SOU rce Category: Ef-

fluent Limitations Guidelines, Pretreatment Standards, and NewSource Performance Standards; Final Rule, Federal Register, vol.49, No. 47, Mar. 8, 1984.

178

Photo credit: Jenifer Robison

Copper tailings have a much finer texture than mine wastes.

miscellaneous wastes include sludges from acidplants (blowdown) and dusts from converters andreverberatory furnaces. Volubility tests have foundthese can leach copper, lead, zinc, and cadmium.They also contain antimony, arsenic, chromium,mercury, nickel, selenium, and silver. Slimes re-covered from electrorefining cells tend to be richin selenium, tellurium, arsenic, gold, silver, andplatinum. The precious metals are recoveredfrom the slime, but significant leaching of haz-ardous constituents from electrolytic refining la-goon sediments is also possible. These sedimentssettle from a combined slurry composed of ef-fluents from spent electrolyte as well as contactcooling of furnaces, spent anode and cathoderinse water, plant washdown, and wet air pollu-tion control.

Reclamation

Reclamation of tailings and mine waste dumpsattempts to restore the area to a productive landuse after closure and to provide long-term envi-ronmental protection. The land use is usually re-stricted to a self-sustaining vegetative cover thatprotects the surface from erosion41 Because mosttailings transport mechanisms depend eitherdirectly or indirectly on water, reclamation tech-niques often focus on controlling and divertingwater.

— —41 Richard C. Barth, “Reclamation Technology for Tailings Im-

poundments Part 1: Containment, ” Mineral and Energy Resources,vol. 29, No. 1, January 1986, p. 2.

179

Tailings transport due to wind erosion also canbe a serious problem, especially when the tail-ings are inactive and dry out. Ambient air stand-ards for total suspended particulate have beenviolated due to the heavy loading of tailings inthe atmosphere.42 This erosion can be controlledby watering the tailings, maintaining a vegetativecover, applying a chemical sealant, or coveringthe tailings with waste rock or slag. In arid cli-mates, waste rock covers are more frequentlyused because revegetation is difficuIt and ex-pensive.

One reclamation technique common to all tail-ings and waste dumps is the application of a layerof topsoil or alluvial material to protect seedlingsfrom glare and supply essential nutrients andmicroorganisms. This technique can be expen-sive; some topsoiling efforts have exceeded$65,000 per acre. Asarco has managed to top-

—.. —— —.12Ge[, rge J. SC h(’~’t’, ,~fonltorlng ‘]ncif ,${o~eling An,]lyws ot’ t h e

Kennec O(I Corpora t ion Sme/ter in ~1( G///, Ne\ ad,], PEDCO Env i -ronmen ta l In( Clnclnnatl, ohlo March 1981,

soil their Arizona tailings successfully for an aver-age cost of $2,500 per acre. 43

Waste Reprocessing and Utilization

Tailings may be reprocessed to recover addi-tional metals. This method may be particularlyrewarding when dealing with older tailing pilesfrom much less efficient beneficiation processes.Tailings also may be used onsite for mine back-fill. There has been extensive research into thepossibility of upgrading tailings to a salable prod-uct such as building materials (e.g., glass andbricks). However, tailings often are unsuitable forsuch materials because they are too fine, havepoor drainage properties, and can be thixotropic(turn liquid when shaken).44

—43Stuart A. Bengson, ‘‘Asarco’s Revegetation of Mill Tailings and

Overburden Wastes from Open Pit Copper Mining operations inArizona, ” paper presented at the National Meeting for the Amer-ican Society for Surface Mine Reclamation, Oct. 8-10, 1985, Den-ver, CO.

44C.G. Down and John Stocks, ‘‘ Positive Uses of Mill TaiIings,

Mining Magazlne, September 1977 pp. 213-223